High temperature solid oxide electrolyte fuel cells are well known in the art and convert chemical energy into direct current electrical energy, typically at temperatures above about 500° C. This temperature is required to render the solid electrolyte sufficiently conductive. Stabilized zirconia is a prime electrolyte. Such fuel cells are taught, for example, by U.S. Pat. No. 4,395,468 (Isenberg). The general working principles and general reactions of a solid oxide fuel cell (“SOFC”) are shown in prior art FIG. 1, which is self-explanatory. Air and a required gaseous fuel, such as natural gas, are both utilized solely to generate electricity at about 800° C. to about 1,000° C. This type SOFC utilizes metal/ceramic fuel electrodes 10, gaseous reformed natural gas fuel and ceramic, dense solid electrolyte 11 and porous ceramic air electrode 12. Fuel 13 is shown by F and oxidant or air A is shown by 14.
An encyclopaedic publication by N. Q. Minh, in Ceramic Fuel Cells, J. Am. Ceramic Soc., 76[3] 563-588, 1993 describes in detail a variety of fuel cell designs, including tubular, triangular and other configurations, as well as materials used and accompanying electrochemical reactions. For example, that article describes segmented cell-in-series (banded and bell-and-spigot), monolithic (co-flow and cross-flow), and flat-plate designs in substantial detail. Cermet fuel electrode (anode) materials, such as nickel or cobalt/yttria stabilized zirconia are also discussed as well as their coefficient of thermal expansion problems.
In addition to generating energy, batteries also store it. Electrical energy storage is crucial for the effective proliferation of an electrical economy and for the implementation of many renewable energy technologies. During the past two decades, the demand for the storage of electrical energy has increased significantly in the areas of portable, transportation, and load-levelling and central backup applications. The present electrochemical energy storage systems are simply too costly to penetrate major new markets, still higher performance is required, and environmentally acceptable materials are preferred. Transformational changes in electrical energy storage science and technology are in great demand to allow higher and faster energy storage at the lower cost and longer lifetime necessary for major market enlargement. Most of these changes require new materials and/or innovative concepts with demonstration of larger redox capacities that react more rapidly and reversibly with cations and/or anions.
Batteries are by far the most common form of storing electrical energy, ranging from: standard every day lead—acid cells, exotic iron-silver batteries for nuclear submarines taught by Brown in U.S. Pat. No. 4,078,125 and nickel-metal hydride (NiMH) batteries taught by Venkatesan et al. in U.S. Pat. No. 5,856,047, Kitayama in U.S. Pat. No. 6,399,247 B1 and Young et al. in U.S. Pat. No. 7,261,970. Also known are metal-air cells taught in U.S. Pat. No. 3,977,901 (Buzzelli), Isenberg in U.S. Pat. No. 4,054,729, U.S. Patent Publications 2006/0063051; 2007/0077491; 2007/0259234 (Jang, Burchardt and Chua et al, respectively) and air batteries also taught in U.S. Patent Publications 2003/0143457 and 2004/0241537 (Kashino et al. and Okuyama et al., respectively). Lithium-ion batteries are taught by Ohata in U.S. Pat. No. 7,396,612 B2.
Batteries range in size from button cells used in watches, to megawatt load levelling applications. They are, in general, efficient storage devices, with output energy typically exceeding 90% of input energy, except at the highest power densities. Rechargeable batteries have evolved over the years from lead-acid through nickelcadmium and nickel-metal hydride (NiMH) to lithium-ion. NiMH batteries were the initial workhorse for electronic devices such as computers and cell phones, but they have almost been completely displaced from that market by lithium-ion batteries because of the latter's higher energy storage capacity. Today, NiMH technology is the principal battery used in hybrid electric vehicles, but it is likely to be displaced by the higher power energy and now lower cost lithium batteries, if the latter's safety and lifetime can be improved. Of the advanced batteries, lithium-ion is the dominant power source for most rechargeable electronic devices.